`--dir .` and `--dir /` conflict with each other

Description

When I run wasmkit run --dir . --dir / <Wasm binary>, it succeeds or fails randomly. When I use --dir .build --dir / or --dir . --dir /Users instead, it always succeeds. So I think --dir . and --dir / conflict with each other.

Steps to reproduce

1. Run mkdir foo && cd foo

2. Run swift package init --type executable

3. Edit Sources/foo/foo.swift

   import Foundation
   
   @main
   struct foo {
       static func main() {
           print(try! String(contentsOf: URL(filePath: #filePath), encoding: .utf8))
           print(Bundle.main)
       }
   }
   

4. Run swift build --swift-sdk swift-DEVELOPMENT-SNAPSHOT-2025-10-02-a_wasm

5. Run wasmkit run --dir . --dir / .build/wasm32-unknown-wasip1/debug/foo.wasm several times

Expected behavior

It succeeds every time. Or it fails every time with the same error messages.

Actual behavior

It always fails, but its error messages randomly change each time it is executed.

Pattern 1:

import Foundation                                                                                                                                    
                                                                                                                                                     
@main                                                                                                                                                
struct foo {                                                                                                                                         
    static func main() {                                                                                                                             
        print(try! String(contentsOf: URL(filePath: #filePath), encoding: .utf8))                                                                    
        print(Bundle.main)                                                                                                                           
    }                                                                                                                                                
}                                                                                                                                                    
                                                                                                                                                     
Error: Trap: unreachable                                                                                                                             
    0: $s10Foundation6BundleC05_mainB033_6273FB07A96EB35BCC520B3A80F5C3CDLL_WZ                                                                       
    1: swift_once                                                                                                                                    
    2: $s10Foundation6BundleC4mainACvgZ
    3: $s3fooAAV4mainyyFZ            
    4: $s3fooAAV5$mainyyFZ
    5: main
    6: __main_void
    7: _start
    8: unknown

Pattern 2:

foo/foo.swift:9: Fatal error: 'try!' expression unexpectedly raised an error: Error Domain=NSCocoaErrorDomain Code=260 "The file doesn’t exist."UserI
nfo={NSFilePath=/Users/kebo/foo/Sources/foo/foo.swift, NSURL=file:///Users/kebo/foo/Sources/foo/foo.swift, NSUnderlyingError=Error Domain=NSPOSIXErro
rDomain Code=44 "No such file or directory"}
Error: Trap: unreachable
    0: $ss17_assertionFailure__4file4line5flagss5NeverOs12StaticStringV_SSAHSus6UInt32VtF
    1: swift_unexpectedError
    2: $s3fooAAV4mainyyFZ
    3: $s3fooAAV5$mainyyFZ
    4: main
    5: __main_void
    6: _start
    7: unknown

Environemnt

$ uname -a
Darwin Xylotrupes-gideon.local 25.1.0 Darwin Kernel Version 25.1.0: Sun Oct  5 21:11:28 PDT 2025; root:xnu-12377.40.120~10/RELEASE_ARM64_T8132 arm64
$ which swift
/Users/kebo/Library/Application Support/swiftly/bin/swift
$ swiftly list
Installed release toolchains
----------------------------
Swift 6.2.0 (default)

Installed snapshot toolchains
-----------------------------
main-snapshot-2025-10-02 (in use)
main-snapshot-2025-09-20
main-snapshot-2025-09-06
$ swift --version
Apple Swift version 6.3-dev (LLVM 0d0246569621d5b, Swift 199240b3fe97eda)
Target: arm64-apple-macosx26.0
Build config: +assertions
$ which wasmkit
/Users/kebo/Library/Application Support/swiftly/bin/wasmkit
$ wasmkit --version
0.1.6

Start by reproducing the issue with the shown wasmkit run --dir . --dir / command and the Swift package example. Trace the directory handling used by the wasmkit run entry point, then verify that repeated runs produce consistent behavior and error messages for overlapping directory arguments.